Method and device for sharpening tools, particularly dental hand instruments

ABSTRACT

A method and apparatus for sharpening tools, particularly hand instruments used in dental care. The apparatus includes a fixed base (19) and a rotary plate (14) fitted thereon, a grinding stone (10) pivoted on an axle (11), and a motor (20) for rotating the grinding stone. According to the invention, adjacent to the circumference (10&#39;) or the side surface (10&#34;) of the grinding stone is fitted a sharpening support (30) which is supported on the rotary plate (14) and on which the instrument to be sharpened rests during sharpening. The rotary plate (14) is arranged rotatively round an axis (41) between the instrument to be sharpened and the sharpening support (30) or through a point in proximity with the contact point.

BACKGROUND OF THE INVENTION

The invention relates to a method and apparatus for sharpening tools,particularly hand instruments for dental care.

About one half of the dental operations are performed with mechanicalinstruments, for example drills, the other half is performed with handinstruments. About one half of the hand instruments are so-calledwearing instruments and the other half are so-called non-wearinginstruments.

Instruments wear most when used for working hard dental enamel anddentin in the removal of damaged tissue for the filling. Theseinstruments are called preparation instruments. They are typicallychisels, flat chisels, chippers and gouges. They are very small in size,0.5-2.0 mm wide. Their blade angle must be and must remain absolutelycorrect after each sharpening.

Instruments wear the second most when used for scaling hard coatings,tartar and cement from the teeth and when root surfaces are beinglevelled. These instruments used for the care of the supportive tissueare typically tartar scalers, general or finishing curets or tartar hookscalers. These are also small in size, the cross-sectional dimensions ofthe blades vary in the range 0.8-1.0 mm. Angles and dimensions must alsoremain unchanged as far as possible after sharpening.

Instruments wear the third most when used for finishing hardened toothfillings and removing excess filling. The instruments of this group aretypically knives and gouges. They are small and thin in shape.

Modern dental instruments are made of stainless steel. They haverelatively poor wear resistance and the blades wear fairly quickly.Therefore, in principle, the wearing instruments should be resharpenedalmost each time after using.

It practice, the most common way of sharpening is grinding with a handgrinding stone. This is, however, a slow and exacting sharpening methodand thus, in practice, it is carried out too seldom. This has theoutcome that a dentist often works with blunt and inefficient tools orthat he tries to omit the hand instrument step. It is obvious that thequality of the work will suffer from this.

To facilitate sharpening of instruments and to make sharpening moreeffective various types of sharpening apparatuses have been developedand manufactured. Following of the known sharpening apparatuses may bementioned:

1) Periostar^(R) (Mikrona Technologia AG)

The structure of the apparatus is described in the patent publication EP307740. The instrument to be ground is fastened by a screw mechanism anda guide mechanism to a bow whereby the blade can be guided in a correctposition against the side of the grinding stone. The tilt angle of thegrinding stone is selected with a control knob and an automatic levermechanism changes the tilt angle when the stone moves from one side ofthe blade to the other. The direction of rotation of the stone changesat the midpoint of the trajectory. A spring mechanism maintains aconstant contact pressure between the blade and the stone duringsharpening.

2) Honing Machine

This apparatus has a to-and-fro moving socket into which the grindingstones of varying shapes and coarseness can be attached according to theneed. The apparatus uses two guide units to show the correct position ofthe blade.

3) LM sharpening device

The apparatus has a sharpening disc which rotates bidirectionally at twospeeds and a self-controlling guide and an instruction card system toaccomplish a correct sharpening position of the instrument.

4) Safident sharpening apparatus

The apparatus has a simple diamond or a ceramic wheel with a shaftlinked directly either vertically or horizontally to the shaft of amotor. The apparatus has no control system whatsoever.

Most of the known apparatuses are not, however, easy to use andefficient at the same time. Operation of some of the apparatusesrequires more expertise than manual sharpening and some apparatuses aretechnically so complicated that the operator cannot master the apparatusor operation is so tedious that the operation cannot be carried out inany realistic time. On the other hand, apparatuses which are too simplespoil small blades with incorrect grinding. When the faults are mended,the steel wears too much and the blade gets thinner and fragile.

SUMMARY OF THE INVENTION

The purpose of this invention is to eliminate the above problem andaccomplish a new method and apparatus without the above drawbacks. Themethod according to the invention is easy and rapid to carry out and theapparatus used in the method has a simple structure and is reliable touse.

The invention relates to a method for sharpening tools, particularlyhand instruments used for dental care, by means of a motor-rotatedgrinding stone. According to the invention the instrument is held inplace in a correct position by supporting it with one hand on anadjustable sharpening support mounted on a rotary plate so that theblade of the instrument to be sharpened touches the circumference or theside surface of the rotating grinding stone. The grinding stone isrotated by moving it with the other hand round such an axis that goesthrough the contact point between the instrument to be sharpened and thesharpening support or a point in proximity with the contact point, thecircumference respectively the side of the grinding stone thereby movingalong the blade to be sharpened. The instrument is kept at such aposition relative to the curved circumference of the grinding stone orthe grinding stone is tilted relative to the plane of the surface of thesharpening support as to obtain exactly the desired tool angle duringsharpening.

The invention also relates to an apparatus for sharpening tools,particularly hand instruments used for dental care, the apparatuscomprising a fixed base and a rotary plate fitted thereon as well as agrinding stone pivoted on an axle. The apparatus further comprises amotor for rotating the grinding stone. The invention is characterized inthat adjacent to the circumference or the side surface of the grindingstone is fitted a sharpening support, which is supported on the rotaryplate and on which the instrument to be sharpened rests duringsharpening. The invention is further characterized in that the rotaryplate is arranged rotatable round an axis which goes through the contactpoint between the instrument to be sharpened and the sharpening supportor through a point in proximity with the contact point.

In the ideal case, said axis goes through the contact point between theinstrument to be sharpened and the sharpening support. However, it is tobe noted that, when sharpening is performed against the circumference ofthe grinding stone pivoted on a horizontal axle, said contact point alsomoves in horizontal direction, when the sharpening support is raised orlowered, so that said axis will no more go through the said contactpoint. It could be possible to arrange the location of the axis to bemovable in horizontal direction, for example so that the location of theaxis in the fixed base is transferable or so that the location of thegroove or hole corresponding to the axis in the rotary plate isselectable. In practice however, the apparatus works satisfactorilyalthough said contact point slightly deviates from the location of theaxis in the horizontal direction. Tests with a grinding stone with adiameter of 50 mm have shown that the horizontal deviation can be in therange 0-5 mm. The term "in the proximity of the contact point", whichalso appears in the claims, means that the perpendicular distancebetween the axis and the instrument/sharpening support contact point canbe 0-5 mm.

According to a preferred embodiment the axis round which the rotaryplate revolves stands in a vertical plane.

The axis round which the rotary plate revolves need not in practicedenote a physical axle stub or extension of a physical axle stub but itmay denote merely a theoretical axis.

According to another preferred embodiment the grinding stone is rigidlyattached to the axle on which it rotates and the ends of the axle aremounted on bearings on axle supports attached to the rotary plane.

According to yet another preferred embodiment the driving unit of thegrinding stone is a motor-rotated, spring-loaded drive wheel extendingfrom the motor to the side or circumference of the grinding stone andpressing against the side or circumference of the grinding stone.

According to yet another preferred embodiment the axle of the grindingstone is located on the axle of the motor and that the motor issupported on a bow with its both ends rotatably mounted on bearings onboth sides of the grinding stone on axle which goes through the diameterof the grinding stone. Consequently, since sharpening of an instrumentis performed against the side surface of the grinding stone, thissolution enables one to arrange adjustable tilting of the grinding stonerelative to the plane of the surface of the sharpening support. Adesired tool angle is obtained by selecting a suitable tilt.

According to yet another preferred embodiment the sharpening support isadjustable into at least two predetermined constant positions, forexample so that a measure L₁ of the sharpening support corresponds toone constant height and its measure L₂ corresponds to another desiredconstant height and the bottom of the sharpening support has recesses inthe bottom and in the side which correspond to pins in the rotary plate.Thus height adjustment is performed by simply turning the sharpeningsupport. According to another alternative, a separate piece is used asthe sharpening support which corresponds to one of the two desiredconstant heights. This kind of separate piece is preferably hinged tothe actual sharpening support.

According to a preferred embodiment the rotary plate does not form abase, on which the components like the grinding stone, sharpeningsupport etc. are supported, but the rotary plate forms a protecting domeat least partly covering the components. In this case the grinding stoneand the other components are suspended from the rotary plate. This kindof dome-like rotary plate can be linked to an axle stub on a fixed baseby means of a diametral bar fitted below the rotary plate, for instance.More preferably, the rotary plate is mounted on bearings on the fixedbase by means of a ball ring in the periphery of the rotary plate.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in the following with reference to theenclosed drawings in which

FIG. 1 shows one embodiment of the apparatus of the invention as aperspective view,

FIG. 2 shows a second embodiment of the apparatus of FIG. 1,

FIG. 3 shows the fixed base as a perspective view,

FIG. 4A and 4B show a third embodiment of the apparatus of theinvention,

FIG. 5 shows fitting of the rotary plate of the apparatus to a rigidbase as a cross-section according to one embodiment,

FIG. 6 shows the sharpening support of the apparatus as a perspectiveview according to one embodiment,

FIG. 7 shows joining of the sharpening support of FIG. 6 to the rotaryplate as a cross-section,

FIG. 8A and 8B show the position of one type of instrument insharpening,

FIG. 9A and 9B show the position of a second type of instrument insharpening,

FIG. 10A and 10B show the position of a third type of instrument insharpening,

FIG. 11 shows the position of a fourth type of instrument in sharpening,

FIG. 12 shows a fourth embodiment of the apparatus of the invention as across-section,

FIG. 13 shows the apparatus of FIG. 12 seen from above,

FIG. 14 shows the apparatus of FIG. 12 provided with a hand support seenfrom the side

FIG. 15 shows the apparatus of FIG. 14 seen from above.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows one embodiment of the apparatus of the invention as aperspective view. On top of a fixed base 19 a rotary plate 14 is fitted,which is arranged freely rotatable to both directions even through 360degrees so that the rotary plate 14 is mounted on bearings on a verticalaxle stub 40 on the fixed base 19 (the axle stub is not shown in FIG.1). The grinding stone 10 of the apparatus is pivoted on an axle 11. Thegrinding stone 10 is rigidly attached to the horizontal axle 11 with itsends mounted on bearings 12, 12' on axle supports 13, 13 attached to therotary plate 14. The motor 20 is a DC motor with a stepless speedcontrol so that the rotational speed of the grinding stone 10 can bevaried in the range 500-1000 RPM. The reference numeral 22 denotes anadapter containing a transformer and a rectifier. The driving unit ofthe grinding stone is a motor-rotated, spring-loaded drive wheel 21extending from the motor 20 to the side surface 10" of the grindingstone and pressing against the side surface 10". Adjacent to thecircumference 10' of the grinding stone is fitted a sharpening support30 supported on the rotary plate 14. Throughout the sharpening operationthe instrument to be sharpened is held in place in a correct position bysupporting it with one hand on the sharpening support 30 so that theblade of the instrument to be sharpened touches the circumference 10' ofthe rotating grinding stone. The rotary plate 14 is arranged rotatableround an axis 41 which goes through the contact point 43 between theinstrument to be sharpened and the sharpening support 30 or through apoint in proximity with the contact point 43. The contact point 43 canbe seen more clearly in FIG. 8B. The apparatus can be protected with aprotective dome not drawn in FIG. 1.

In this solution, the grinding stone is rigidly fixed to the axle withits ends mounted on bearings 12, 12' on axle supports 13, 13 attached tothe rotary plane 14. The bearing housings of the axle supports 13, 13'have an open structure. This kind of open bearing structure togetherwith the described solution for driving the grinding stone makesreplacement of the grinding stone rapid and simple.

FIG. 2 shows a second embodiment of the apparatus of FIG. 1. Thesharpening support 30 abuts on a raised part 60 on the rotary plate. Thereference numeral 61 denotes an adjustment screw by which the sharpeningsupport against the grinding stone 10 is adjusted. The referencenumerals 70 and 71 denote brushes from which electric wires go to themotor 20. The lower surfaces of the brushes make contact with copperrings 75, 76 fitted on the upper side of the fixed base (FIG. 3), towhich electricity is conducted from the mains via an adapter 22, one ofthem corresponding to the + terminal and the other the - terminal. Thedriving wheel, which is attached to the motor, has not been drawn in thefigure.

FIGS. 4A and 4B show a third embodiment of the apparatus of theinvention. FIG. 4A shows the apparatus as a perspective view and FIG. 4Bshows the apparatus seen from above. The axle 11 of the grinding stone10 is located on the axle of the motor 20 and the motor 20 is supportedon a bow 51 with its both ends 52, 52' rotatably mounted on bearings onboth sides of the grinding stone on an axis 50 which goes diametricallythrough the grinding stone. In this solution, sharpening is performedagainst the side surface 10" of the grinding stone. The tilt angle Γ ofthe grinding stone relative to the surface of the sharpening support 30is adjustable in this solution. By choosing a correct tilt angle Γ, whensharpening is performed against the side surface 10" of the grindingstone, one obtains a desired tool angle α.

The cross-section of FIG. 5 shows that the rotary plate 14 is mounted onbearings on a vertical axle stub 40 on the fixed base 19. In thissolution the axle stub 40 extends only to a certain distance into therotary plate 14 but it could alternatively extend through the rotaryplate 14. The rotary plate is freely rotatable in both directions.According to one embodiment the electric current required by the motorcan be conducted through wires resting on the fixed base 19 and therotary plate 14 via the axle stub 40 into the motor. In this case theaxle stub 40 has two terminals and is provided with brushes.

FIG. 6 shows the sharpening support 30 located adjacent to thecircumference 10' of the grinding stone which can be adjusted quitesimply into two predetermined constant heights from the plane of therotary plate 14. The measure L₁ of the sharpening support corresponds toone constant height and its measure L₂ corresponds to another constantheight. FIG. 7, shows the recesses 31, 32 and 33, 34 respectively in thebottom and in the side of the sharpening support corresponding to thepins 15 and 16 in the rotary plate 14. Height adjustment is performedsimply by turning the sharpening supports. The measures L₁ and L₂ arechosen suitably to correspond to tool angles (75 and 60 degrees)occurring in most instruments.

Operation of the apparatus becomes apparent in FIGS. 8-11.

FIGS. 8A and 8B present the sharpening of a curet. FIG. 8A shows fromabove the curet K resting on the upper surface of the sharpening support30 so that the blade being sharpened touches the circumference 10' ofthe grinding stone. The working face T is kept horizontal. It is seen inFIG. 8B that the blade being sharpened is raised from the plane of thehorizontal diameter of the grinding stone so that the radius of thegrinding stone drawn from the contact point 42 makes an angle whichcorresponds to the taper angle β of the blade with the horizontalradius. In this way choosing a correct contact point a desired toolangle α (α=90°-β) of the curet is obtained. Since a suitable tool anglea for a curet is 75° one must choose β=15°.

During the sharpening the operator holds the instrument K in place in acorrect position with one hand. Using his other hand he rotates therotary plate together with all the equipment supported thereon round itsaxis 41 to-and-fro along the blade being sharpened. Depending on theshape of the blade he is able to sharpen the edge at three sides withoutlifting the instrument from the sharpening support. If straight blades(chisels etc.) are sharpened, the rotary plate can be held immobile aswell. Sharpening is possible both on the front and back side of thegrinding stone. Both left- and right-handed operation is possible.Although the grinding stone can rotate in both directions on its axle,it is a safer practice to perform the sharpening so that the grindingstone rotates away from the blade in the direction of the arrow in FIG.8B.

FIGS. 9A and 9B show sharpening of a sickle. Also in this case theworking face of the instrument is kept horizontal and β is chosen =15°.Because the front edge of this instrument is very sharp, sharpening isfirst performed on one side of the blade from bottom to edge. Next therotary plate/stone is turned and the other side is sharpenedrespectively.

FIGS. 10A and 10B show sharpening of a levelling instrument. The toolangle α of this type of instrument is suitably 60° so that one mustchoose the height of the sharpening support such that β equals to 30°.To facilitate correct positioning of the instrument the upper surface ofthe sharpening support is provided with pre-drawn lines.

FIG. 11 shows the sharpening of a hook. The tool angle a of this type ofinstrument is also suitably 60°. In order to have a proper support forthis small sized hook H near the grinding stone, an additional part 35which extends nearer to the contact point 42 is fitted on top of thesharpening support 30.

FIG. 12 shows a solution of the apparatus according to the invention asa cross-section in which the rotary plate 14 does not form a base, onwhich the components (the grinding stone 10, sharpening support 30,etc.) are supported, but the rotary plate 14 forms a protective domepartly covering said components. In this solution the grinding stone 10and the other components are suspended from the rotary plate 14. It isnaturally important for the use of the apparatus that the dome-likerotary plate 14 does not entirely cover the grinding stone 10 nor thesharpening support 30. The dome-like rotary plate 14 is shaped so thatthe part of the grinding stone and sharpening support that are essentialto sharpening remain above the surface of the rotary plate. As shown inFIG. 13 the rotary plate 14 is provided with an lead-through opening 65for these components. A recess 17 is formed in the rotary plate intowhich a turning handle of the plate can be embedded. The sharpeningsupport 30 supported on the rotary plate is adjustable in horizontaldirection by means of an adjusting device 37. Height adjustment of thesharpening support is performed by means of an additional part 35 hingedto the edge 36 of the sharpening support 30 which can be readily turnedon top of the sharpening support and off therefrom. The rotary plate 14is mounted on bearings on the fixed base 19 by means of a ball ring 45,45', 45". . . in the periphery of the fixed base. FIG. 12 shows only twoballs 45 and 45' but in practice the number of balls is higher. Thefixed base 19 forms in this solution an annular piece provided withanti-skid stops 18, 18'.

FIGS. 14 and 15 show the apparatus of FIG. 12 provided with a cover 80which partly covers the apparatus and serves as the hand support duringsharpening. The cover 80 is attached to the fixed base 19.

The greatest benefits of the invention are that the apparatus is sosimple that risk for inaccurate sharpening is minimized. The facts thatthe blade to be sharpened needs no mechanical mounting, that manualsupporting and changing is quick and that the accuracy due to thesharpening support is sufficient, make sharpening time per bladerealistically fast, only a few seconds per blade. The contact forceagainst the grinding stone can be adjusted manually which makesadjustment of sharpening rate simple for blades of various hardness anddegree of wear. Sharpening can be readily stopped during sharpening toprevent excess heating of the blade.

The above figures present such a solution in which the axle, round whichthe rotary plate turns, is in a vertical plane. This is in practice themost preferrable embodiment but the invention is not limited to this. Itis also possible that the axle round which the rotary plate turns is ina horizontal plane.

Although the above description deals with the use of the apparatus forsharpening tools used for dental care, it will be understood that theapparatus also suits to sharpening of other tools. In particular, it issuitable for such tools used in precision mechanics which have blades tobe sharpened on more than one side or in which the blades are curved ortilted.

It is obvious to a specialist in the field that the various embodimentsof the invention can vary within the limits of the enclosed claims.

I claim:
 1. An apparatus for sharpening objects, comprisingi) a fixedbase; ii) a plate rotatively mounted on said base and having an axis ofrotation through a center of said plate; iii) a grinding stonerotatively mounted on said plate, said grinding stone having a shape ofa disc with two sides, a circumference, and a central axis of rotationnormal to said sides; iv) a motor operatively connected to said grindingstone for imparting rotation about said central axis of rotation of saidgrinding stone; and v) a support for an object to be sharpened, saidsupport mounted on said plate adjacent either said circumference or oneof said sides of said grinding stone such that a contact point isdefined between the object to be sharpened and either said circumferenceor said side; with the proviso that said axis of rotation of said plateextends through said contact point or through a point in proximity withsaid contact point.
 2. The apparatus of claim 1, wherein said axis ofrotation of said plate is vertical.
 3. The apparatus of claim 1, whereinsaid grinding stone is rigidly attached to an axle rotatively supportedon bearings operatively mounted on said plate.
 4. The apparatus of claim1, wherein said motor is connected to said grinding stone by a drivingwheel which extends from said motor and which is urged against said sideor circumference of said grinding stone by a spring.
 5. The apparatus ofclaim 1, wherein said grinding stone is rigidly attached to an axle ofsaid motor, and wherein said motor is supported on a bow whose ends arerotatively mounted on bearings on both sides of said grinding stone onan axis which goes diametrically through said grinding stone.
 6. Theapparatus of claim 1, wherein said support for an object to be sharpenedhas at least two predetermined fixed positions.
 7. The apparatus ofclaim 6, further comprising an additional height adjustment member whichis pivotably mounted on said support for an object to be sharpened suchthat said member can move onto or from the top of said support.
 8. Theapparatus of claim 1, wherein said plate is rotatively mounted by aplurality of ball bearings on said fixed base in a ball ring on aperiphery of said plate.
 9. The apparatus of claim 1, wherein said motoris a DC motor with a stepless speed control.
 10. A method for sharpeningobjects, comprising the steps of:providing the apparatus of claim 1,maintaining an object to be sharpened in position on said support for anobject to be sharpened such that a point of contact is created between asurface of said object and the circumference or side surface of saidgrinding stone while said stone is rotating; rotating said plate andthereby said grinding stone about said axis of rotation of said plate,thereby moving said point of contact along a surface of the object to besharpened, wherein said object is maintained in such a position relativeto the curved circumference of said grinding stone, or the grindingstone is tilted relative to a plane of said support for an object to besharpened such that the desired angle of sharpening of said object isachieved.
 11. The method of claim 10, wherein the force applied to urgethe object against the grinding stone and the time of contact of theobject and said stone are manually controlled.
 12. An apparatus forsharpening objects, comprisingi) a fixed base; ii) a dome rotativelymounted on said base and having an axis of rotation through a center ofsaid dome; iii) a grinding stone rotatively suspended from said dome,said grinding stone having a shape of a disc with two sides, acircumference, and a central axis of rotation normal to said sides; iv)a motor operatively connected to said grinding stone for impartingrotation about said central axis of rotation of said grinding stone; andv) a support for an object to be sharpened, said support suspended fromsaid dome adjacent either said circumference or one of said sides ofsaid grinding stone such that a contact point is defined between theobject to be sharpened and either said circumference or said side;withthe proviso that said axis of rotation of said dome extends through saidcontact point or through a point in proximity with said contact point,and with the further proviso that said dome does not entirely cover saidgrinding stone or said support for an object to be sharpened.